Side dam with insert

ABSTRACT

A composite side dam for a continuous twin roll caster includes a substrate made of a refractory material capable of withstanding casting temperature and having edge portions adapted to engage casting rolls and having a nip portion adjacent a nip between casting rolls and upper portions extending across the side dam to form a lateral restraint for a casting pool, an insert of at least 10 mm in thickness positioned in a pocket in the substrate and extending to engage the molten metal and extending from the upper portions of the substrate and positioned in the pocket to within 30 mm from the nip portion by insertion adjacent the upper portions of the substrate, and the insert adapted to fit into the pocket of the substrate to form a side dam formed of a refractory material having consumption rate less than 10 mm per hour. The material forming the insert may be between 40 and 60% SiAlON material and the remainder hBN material, or mullite material as described by FIG.  11,  or between about 60 and 63 mole percent Al 2 O 3  and the remainder SiO 2 , or fused silica, such as between 40 and 60% fused SiO 2  and the remainder hBN material.

BACKGROUND AND SUMMARY

This invention relates to the casting of metal strip by continuous casting in a twin roll caster.

In a twin roll caster, molten metal is introduced between a pair of counter-rotated casting rolls that are cooled so that metal shells solidify on the moving roll surfaces and are brought together at a nip between them. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be delivered from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle located above the nip, forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. As the molten metal formed into shells are joined and pass through the nip between the casting rolls, a thin metal strip is cast downwardly from the nip.

The casting pool is usually confined between side dams held in sliding engagement with end surfaces of the casting rolls so as to constrain the two ends of the casting pool against outflow. Side dams at the ends of the casting rolls prevent leakage of molten metal from the casting pool and maintain the casting pool at a desired depth. As the casting rolls are rotated, the side dams experience frictional wear, causing arc-shaped grooves to form in the side dams along the circumferential surfaces of the casting rolls. In order to compensate for this wear, the side dams are movable to gradually shift inward under compression forces while having the side dams biased against the ends portions of the casting rolls in order to maintain a seal with the casting rolls.

When casting steel strip in a twin roll caster, the thin cast strip leaves the nip at very high temperatures, of the order of 1400° C. If exposed to normal atmosphere, it will rapidly form scale by oxidation at such high temperatures. A sealed enclosure that contains an atmosphere that inhibits oxidation of the strip is therefore provided beneath the casting rolls to receive the thin cast strip, and through which the strip passes away from the strip caster. The oxidation inhibiting atmosphere may be created by injecting a non-oxidizing gas, for example, an inert gas such as argon or nitrogen, or combustion exhaust reducing gases. Alternatively, the enclosure may be substantially sealed against ingress of an ambient oxygen-containing atmosphere during operation of the strip caster, and the oxygen content of the atmosphere within the enclosure is reduced during an initial phase of casting, by allowing oxidation of the strip to extract oxygen from the sealed enclosure as disclosed in U.S. Pat. Nos. 5,762,126 and 5,960,855.

The length of a casting campaign of a twin roll caster has been generally determined in the past by the useful life of the core nozzle, tundish and side dams. Multi-ladle sequences can be continued by use of a turret allowing sequential ladles of molten metal to be transferred to the operating position. The focus in extending casting campaigns, therefore, has been extending the useful life of the core nozzle, tundish and side dams, and in turn reducing the cost per ton of casting thin strip. Wear and replacement of the side dams has usually limited the casting campaign, where the casting campaign was typically stopped and the worn side dams replaced. The core nozzles and tundish with remaining useful life were typically replaced at the same time so the length of the next campaign is not limited, with attendant waste of useful life of refractories and increased cost of casting steel. In the past, one focus has been on improving refractory materials. Graphitized alumina, boron nitride and boron nitride-zirconia composites are examples of suitable refractory materials for the side dams, tundish and core nozzle components. SiAlON (i.e, silicon alumina oxy-nitride) refractory material has also been proposed for use in making side dams.

Also, the side dams wear independently of the core nozzles and tundish, and independently of each other. The side dams must initially be urged against the ends of the casting rolls under biasing forces, and “worn-in” to be adequately seated against outflow of molten steel from the casting pool. The biasing forces applied to the side dams may be reduced after an initial wear-in period, but there continued to be significant wear of the side dams throughout the casting operation. The useful life of the side dams has remained a limiting factor in the length of casting campaigns and the cost of casting thin strip. The core nozzle and tundish components in the metal delivery system could have a longer life than the side dams, and could normally continue operating through several additional ladles of molten steel supplied extending the casting campaign and dramatically reducing the cost of casting thin strip.

Disclosed is a composite side dam for a continuous twin roll caster substantially increasing the use life of the side dams and reducing the cost of casting thin strip. The composite side dam comprises a substrate shaped to form a side dam and made of a refractory material capable of withstanding casting temperature in a twin roll caster. The substrate has edge portions adapted to engage end portions of casting rolls, and has a nip portion adapted to be adjacent a nip between casting rolls and has upper portions extending cross the side dam to form a lateral restraint for a casting pool of molten metal during operation in a twin roll caster. An insert of at least 10 mm in thickness is positioned in a pocket provided in the substrate to engage the molten metal in operation of a twin roll caster and extend from the upper portions of the substrate to within 30 mm from the nip portion of the substrate, by insertion adjacent the upper portions of the substrate to engage end portions of the casting rolls during operation of the twin roll caster. The insert is adapted to fit into the pocket of the substrate to form a side dam formed of a refractory material having consumption rate less than 10 mm per hour.

The material forming the insert may be comprised of SiAlON material and may be between 20 and 60% SiAlON material and the remainder may be hBN (i.e, hexagonal boron nitride) material. The material forming the insert alternatively may be comprised of mullite material defined by FIG. 11 (between about 60 and 63 mole percent Al₂O₃ and the remainder SiO₂). The material forming the insert also alternatively may be comprised of fused silica material between 20 and 60% fused SiO₂ and the remainder hBN. The consumption rate due to contact with molten metal of the refractory material forming the insert may be at least as great as the wear rate due to abrasive contact with the casting rolls of the material forming the substrate.

The insert may be between 10 mm and 40 mm in thickness, and may have a thickness greater than a depth of the pocket in the substrate. The insert may have edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate. Further, the insert may have a firm fit in the pocket of the substrate. Alternatively or in addition, the insert may be positioned in the pocket of the substrate with a ceramic cement. Additionally, the insert may extend toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G illustrate various aspects of an exemplary continuous twin roll caster system.

FIG. 2 illustrates an exemplary embodiment of a side dam holder, used in the system of FIGS. 1A-1G.

FIG. 3A is a front view of a side dam used in the system of FIGS. 1A-1G.

FIG. 3B is a top view of the side dam shown in FIG. 3A.

FIG. 3C is an isometric view showing the back side of the side dam shown in FIG. 3A.

FIG. 4 is an exploded assembly view of the side dam of FIGS. 3A-3C.

FIG. 5 is a back view of two actual side dams previously used similar to the side dam of FIGS. 3A-3C.

FIG. 6 is a front view of the two side dams shown FIG. 5 after use in a twin roll caster system.

FIG. 7 is an enlarged view of a portion of one of the side dams shown in FIG. 6.

FIG. 8 is a table reporting measured number of snake eggs with each coil of thin cast strip through a number of heats in a casting campaign adjacent the operator side and drive side side dams with previous side dams and the presently described side dams.

FIG. 9 is a graph showing snake eggs recorded during the casting campaign reported in FIG. 8, along with coil sequence during the campaign.

FIG. 10 shows two actually used side dams: on the left a side dam of a previous design and on the right a side dam of the present invention taken during the same casting sequence.

FIG. 11 is a graph defining mullite material for the present invention.

FIG. 12 shows two graphs comparing the number of snake eggs in a casting campaign using previous side dams and composite side dams of the present invention.

FIG. 13 shows two graphs comparing the number of snake eggs in a casting campaign using previous side dams and composite side dams of the present invention.

FIG. 14 shows two graphs comparing the number of snake eggs in a casting campaign using previous side dams and composite side dams of the present invention.

DETAILED DESCRIPTION

FIGS. 1A-1G illustrate various aspects of an exemplary continuous twin roll caster system. The illustrative twin roll caster comprises a twin roll caster denoted generally as 11 producing a cast steel strip 12 which passes within a sealed enclosure 10 to a guide table, which guides the strip to a pinch roll stand 14 through which it exits the sealed enclosure 10. The seal of the enclosure 10 may not be complete, but appropriate to allow control of the atmosphere within the enclosure and limit access of oxygen to the cast strip within the enclosure as hereinafter described. After exiting the sealed enclosure 10, the strip may pass through other sealed enclosures and may be subjected to in-line hot rolling and cooling treatment.

Twin roll caster 11 comprises a pair of laterally positioned casting rolls 22 forming a nip 15 there between, to which molten metal from a ladle 23 is delivered through a metal delivery system 24. Metal delivery system 24 comprises a tundish 25, a removable tundish 26 and one or more core nozzles 27 which are located between the casting rolls above the nip 15. The molten metal delivered to the casting rolls forms casting pool 16 supported on the casting surfaces of the casting rolls 22 above the nip 15. The casting pool of molten steel is confined at the portions ends of the casting rolls 22 by a pair of side dams 35, which engage the end portions of the rolls by operation of a pair of hydraulic cylinder units 36 acting through thrust rods 50 connected to side dam holders 37.

The casting rolls 22 are internally water cooled by coolant supply and driven in counter rotational direction by drives, so that metal shells solidify on the moving casting roll surfaces as the casting surfaces move through the casting pool 16. These metal shells are brought together at the nip 15 to produce the thin cast strip 12, which is delivered downwardly from the nip 15 between the rolls.

Tundish 25 is fitted with a lid 28. Molten steel is introduced into the tundish 25 from ladle 23 via a shroud 29. The tundish 25 is fitted with a slide gate valve 34 to selectively open and close the outlet 31 and effectively control the flow of metal from the tundish to the removable tundish 26. The molten metal flows from tundish 25 through an outlet 31 through a shroud 29 to removable tundish 26 (also called the distributor vessel or transition piece), and then to core nozzles 27. At the start of a casting operation a short length of imperfect strip is produced as the casting conditions stabilize. After continuous casting is established, the casting rolls are moved apart slightly and then brought together again to cause the leading end of the strip to break away so as to form a clean head end of the following cast strip to start the casting campaign. The imperfect head end of the strip drops into a scrap box receptacle 40 located beneath caster 11 and forming part of the enclosure 10 as described below. At this time, swinging apron 38, which normally hangs downwardly from a pivot 39 to one side in enclosure 10, is swung across the strip outlet from the nip 15 to guide the head end of the cast strip onto guide table 13, which feeds the strip to the pinch roll stand 14. Apron 38 is then retracted back to its hanging position to allow the strip to hang in a loop beneath the caster, as shown in FIGS. 1B and 1D, before the strip passes to the guide table where it engages a succession of guide rollers.

The twin roll caster illustratively may be of the kind which is illustrated in some detail in U.S. Pat. Nos. 5,184,668 and 5,277,243, and reference may be made to those patents for appropriate constructional details.

Referring to FIGS. 1E and 1G, the support assembly for the side dams 35 is shown. The first enclosure wall section 41 surrounds the casting rolls 22 and is formed with side plates 64 provided with cut-out shaped to snugly receive and support the side dam plate holders 37, which in turn support the side dams 35 that are pressed against the ends portions of casting rolls 22 by the cylinder units 36. The interfaces between the side dam holders 37 and the enclosure side wall sections 41 are sealed by sliding seals 66 to maintain sealing of the enclosure 10. Seals 66 may be formed of ceramic fiber rope or other suitable sealing material. The cylinder units 36 extend outwardly through the enclosure wall section 41, and at these locations the enclosure is sealed by sealing plates 67 fitted to the cylinder units so as to engage with the enclosure wall section 41 when the cylinder units are actuated to press the pool closure plates against the ends of the casting rolls. Cylinder units 36 also move refractory slides 68 which are moved by the actuation of the cylinder units to close slots 69 in the top of the enclosure, through which the side dams 35 are initially inserted into the enclosure 10 and into the holders 37 for application to the casting rolls. The top of the sealed enclosure 10 is closed by the tundish 26, the side dam holders 37 and the slides 68 when the cylinder units are actuated to urge the side dams 35 against the casting rolls 22.

When it is determined that the side dams 35 need to be change, typically due to wear, a preheating sequence is commenced. The core nozzle 27 and the removable tundish 26 are also typically replaced at the same time. This preheating of the second tundish 26′ and second core nozzle 27′ is started while casting is continuing at least 2 hours before transfer to the replacement sequence, and the preheating of the second side dams 35′ is started at least 0.5 hours before transfer to the replacement sequence. This preheating is done in preheating heaters 50, 54 and 57, typically preheating chambers, in locations convenient to the caster 11, but removed from the operating position of the refractory components during casting.

During this preheating of the replacement refractory component, casting typically continues without interruption. When the refractory component to be replaced (namely, the tundish 26, the core nozzle 27 and the side dams 35), the slide gate 34 is closed and the tundish 26, the core nozzle 27 and the casting pool 16 are drained of molten metal. Typically, the tundish 26′ and side dams 35′ are preheated and replaced as individual refractory components, and the core nozzle is preheated and replaced as a singular or two piece refractory component, but in particular embodiments may be preheated and replaced in pieces or parts as those portions of the refractory component are worn or otherwise need to be replaced.

When the preheating is completed and the change in side dams is to take place, the slide gate 34 is closed and the tundish 26, core nozzle 27 and casting pool 16 are drained and casting is interrupted. A pair of transfer robots 55 remove the first side dams 35 from the operating position, and then a pair of transfer robots 56 transfer the second side dams 35′ from the preheating chamber 57 to the operating position. Note that transfer robots 55 and 56 may be the same as shown in FIG. 1A if there is a place for the transfer robots to rapidly set aside the removed first side dams 35. However, to save time in removing the side dams 35 and positioning the second side dams 35′ in the operating position, two pairs of transfer robots 55 and 56 may be employed. Following positioning of the second side dams 35′ in the operating position, the side gate 34 is opened to fill the tundish 26 and core nozzle 27 and form casting pool 16, and continue casting.

Each transfer robot 55 and 56 is a robot device known to those skilled in the art with gripping arms 70 to grip the core nozzle 27 or 27′ typically in two parts, or side dams 35 or 35′. The transfer robots can be raised and lowered and also moved horizontally along overhead tracks to move the core nozzle or the side dams from a preheating chamber at a separate location from the operating position to the caster for downward insertion of the plates through the slots 69 into the holders 37. Gripping arms 70 are also operable to remove at least portions of worn core nozzle 27 or side dams 35. The step of removing the worn side dams 35 is done by operating cylinder unit 36 to withdraw the thrust rod 50 sufficiently to open the slot 69 and to bring side dam 35 into position directly beneath that slot, after which the gripping arm 70 of the transfer robot 55 can be lowered through the slot to grip the side dam 35 and then raised to withdraw the worn side dam. The side dams 35 may be removed when they become worn to specified limits as will be explained further below, and may be removed one at a time as worn to a specified limit. During a casting run and at a time interval before the side dams 35 have worn down to an unserviceable level, the wear rate of the side dams 35 may be monitored by sensors, and the preheating of replacement side dams 35′ is commenced in preheat furnaces at preheating chamber 57 separate from the caster 11.

To change the side dams 35, when the molten steel is drained from the metal delivery system and casting pool, cylinder units 36 are operated to retract the side dam holders 37 and to bring the side dams 35 directly beneath the slots 69 which are opened by the retraction movement of the slides 68. Transfer robots may then be lowered such that their gripping arms 70 can grip the side dams 35 and raised and remove those worn side dams, which can then be dumped for scrap or refurbishment. The transfer robots are then moved to the preheat chambers where they pick up the replacement side dams 35′ and move them into position above the slots 69 and the retracted side dam holders 37. Side dams 35′ are then lowered by the transfer robots into the plate holders, the transfer robots are raised and the cylinder units 36 operated to urge the preheated replacement side dams 35′ against the end of the casting rolls 22 and to move the slides 68 to close the enclosure slots 69. The operator then actuates slide gate 34 to initiate resumption of casting by pouring molten steel into tundish 26 and core nozzle 27, to initiate a normal casting operation in a minimum of time.

It may be desirable to replace a side dam or dams 35 when worn to specified limits, such as when the dam(s) become or will become unserviceable. For example, the wear of the side dams may be monitored by means of load/displacement transducers mounted on cylinders 36. The cylinders will generally be operated so as to impose a relatively high force on the side dams 35 during an initial bedding-in period in which there will be a higher wear rate after which the force may be reduced to a normal operating force. The output of the displacement transducers on cylinders 36 can then be analyzed by a control system, usually including a computerized circuit, to establish a progressive wear rate and to estimate a time at which the wear will reach a level at which the side plates become unserviceable. The control system is responsive to the sensors to determine the time at which preheating of replacement side dams must be initiated prior to interrupting the cast for replacement of the side dams.

FIG. 2 illustrates an exemplary embodiment of a side dam holder 37 for use in the continuous casting system. The side dam holder 37 is used in the system of FIGS. 1A-1G, in accordance with various aspects. The side dam holder 37 includes three attachment portions 210, 220, and 230. In the embodiment shown in FIG. 2, the attachment portions 210, 220, and 230 are notches or troughs (typically stainless steel) that are capable of receiving and supporting a side dam without exposed portions of the side dam holder 37 extending substantially beyond an outer surface of the side dam adjacent the side dam holder.

A composite side dam 35 for the continuous twin roll caster 11 embodying the present invention is shown in FIGS. 3A, 3B, and 3C. The composite side dam comprises a substrate 72 shaped to form a side dam and made of a refractory material such as boron nitride zirconium capable of withstanding casting temperatures in a twin roll caster. The substrate 72 has edge portions 74 adapted to engage end portions of casting rolls 22, and has a nip portion 76 adapted to be adjacent the nip 15 between casting rolls 22. The substrate also has a pocket 82 into which an insert 80 is fitted as described below, and has upper portions 78 extending cross the pocket 82 of side dam 35 to form a lateral restraint for a casting pool 16 of molten metal during operation in the twin roll caster 11.

FIG. 4 is an exploded assembly view of the side dam of FIGS. 3A-3C illustrating the assembly of the insert 80 into the pocket 82 of the substrate 72.

FIGS. 5, 6 and 7 show side dams as shown in FIGS. 3A-3C showing how the side dams wear with use in a campaign to make thin strip in a twin roll caster. Specifically, FIG. 5 shows a back view of a pair of actual side dams similar to the side dam illustrated in FIGS. 3A-3C previously used in a casting campaign to make thin steel strip. FIG. 6 is a front view of the pair of side dams shown in FIG. 5 after use in a campaign in a twin roll caster to make thin steel strip. And FIG. 7 is an enlarged view of a portion of one of the side dams shown in FIG. 6 showing a close up of the wear adjacent nip 15 of the side dam after use in a casting campaign.

As shown in FIGS. 3A through 7, the insert 80 is of at least 10 mm in thickness and may be positioned in a pocket 82 in the substrate 72. The insert 80 is adapted to engage molten metal in the casting pool in operation of the twin roll caster 11. The insert 80 extends from the upper portions engaging upper portions 78 of substrate 72 such that the insert 80 can be positioned in the pocket 82 to within 30 mm from the nip portion 76 (as shown in FIG. 7) by insertion adjacent the upper portions 78 of the substrate 72 as shown in FIG. 4, and adapted to engagement of the casting rolls 22 during operation of the twin roll caster 11. The insert 80 may extend to between 15 to 25 mm from the nip portion 76 of the substrate 72, and in any event, may extend toward the nip portion 76 to allow at least a 2.5 mm radius R in the insert 80 adjacent nip portions of the side dam 35.

The insert 80 is formed of a refractory material that may have a consumption rate less than 10 mm per hour, and in any event, at least as great as the consumption rate to the substrate 72. The material forming the insert 80 comprises a SiAlON material. The material forming the insert 80 may be between 20 and 60% SiAlON material and the remainder hBN material. In another embodiment the material forming the insert 80 alternatively may be comprised of mullite material defined by FIG. 11 (between about 60 and 63 mole percent Al₂O₃ and the remainder SiO₂). In a further embodiment, the material forming the insert 80 may be between 20 and 60% fused SiO₂ and the remainder hBN material. The consumption rate of the refractory material forming the insert 80 should be at least as great as the wear rate of the material of the refractory forming the substrate 72.

As shown in FIG. 4, the insert 80 may have a thickness between 10 mm and 40 mm. The insert 80 also may have a thickness greater than a depth of the pocket 82 in the substrate 72. The insert 80 may have edge portions 84 of a reverse angle J of at least 3° to engage edge portions 86 of the pocket 82 in the substrate 72. The reverse angle J may be between 3° and 5°. The insert 80 may form a firm fit when positioned in the pocket 82 so that the insert 80 is held in position to form with the substrate 72 the composite side dam 35 without ceramic cement or other adherent binder. Alternatively, the insert 80 may also have a ceramic pin or screw 88 as shown in FIG. 5 extending through the substrate 72 into the insert 80 to hold the insert 80 in firm engagement with substrate 72. Also, in addition or in the alternative, the insert 80 may be held in position in the pocket 82 with a ceramic cement.

Generally, in campaigns in casting thin strip, solidified skulls may form from time to time adjacent the side dam and also the delivery nozzle when the distance between the side dam and nozzle is not maintained. These skulls may also be formed on the side dams surfaces protruding into the casting pool beyond the casting rolls surfaces. When these skulls drop through the roll nip, they may cause the two solidifying shells at the casting roll nip to separate and “swallow” additional liquid steel between the shells causing the strip surface to reheat and, in extreme cases, may cause the strip to break disrupting the continuous production of coiled strip. These dropped skulls formed in the cast strip are known as “snake eggs.” In any event, snake eggs can cause defects to occur in the cast strip. The snake eggs are detected as lateral force spikes on the side dams at the roll nip, as well as visible bright bands across the width of the cast strip. Snake eggs usually apply resistive forces against the side dam, in addition to the forces on the side dam generated by the ferrostatic head in the cast pool, and can cause the side dam to lift from the casting roll edge resulting in the leakage of steel between the side dam and the casting roll. Snake eggs passing through the nip between the casting rolls may cause lateral movement of the casting rolls along with upward movement in the side dams. To resist the increased forces generated by the snake eggs, the side dams are typically biased toward the casting rolls with appropriate higher lateral forces.

An advantage of the present invention can be seen by FIGS. 8 and 9. FIG. 8 shows the snake egg count adjacent the side dams and the protruding surfaces of the side dams on both the operator side and the drive side of the caster for each coil during the casting campaign. As shown in FIGS. 8 and 9, measurements were taken and reported on both the drive side and the operator side of snake eggs of more than 2 kN in force, more than 3 kN in force, and more than 5 kN in force. As indicated by the brackets, during the first part of the campaign the side dams were of the previous design of solid refractory, and during the latter part of the campaign composite side dams of the present invention were employed. As shown by FIG. 8, snake egg numbers as high as 50, 60 and 111 of force greater than 2 kN were reported for coils where side dams of the previous solid design were used. Whereas, snake egg numbers never greater than 9 or 11 were reported where composite side dams of the present invention were used. Note that with both of the side dams of the previous design and side dams of the present invention the larger numbers of snake eggs occurred toward the end of the use of the side dam. FIG. 9 graphically shows the increase in both amplitude and number of the snake eggs between using the side dams of the previous solid design and composite side dams of the present invention.

FIG. 10 shows the difference in textures of the side dam, on the left of the previous solid design and of the side dam on the right of the presently disclosed composite design. These two side dams were employed and used in the same casting campaign so a direct comparison could be made. As seen by comparison, the texture of the wear on the composite side dam is more even with the present composite side dams than the wear on the previous side dam of a solid design.

Referring to FIGS. 12, 13, and 14, a comparison of the snake eggs count adjacent to the side dam at the start up of the sequence and at the tail out of the sequence when using side dams of a previous design and composite side dams of the current invention is shown. In FIG. 12 is shown the average snake egg count and spread of snake eggs where the force exerted by the snake eggs in roll separation is greater than 2 kN for the previous standard of solid side dams (as described above) and the composite sides of the present invention. In FIG. 13 is shown the average snake egg count and the spread of snake eggs where the force exerted by the snake eggs is between 3 and 5 kN for the previous standard of solid side dams (as described above) and the composite sides of the present invention. And in FIG. 14 is shown the average snake egg count and spread of snake eggs where the force exerted by snake eggs is greater than 5 kN for the previous standard of solid side dams (as described above) and the composite sides of the present invention. In each case, the number of snake eggs and the force spread exerted by the snake eggs was greatly reduced with use of the composite side dams of the present invention.

Specifically, in FIG. 12 an average of 70 snake eggs and a spread of 65 to 75 snake eggs of greater than 2 kN force were reported for campaigns where side dams of the previous solid design (or standard) were used. Whereas, the average number of snake eggs was 8 and a spread of 5 to 15 snake eggs of greater than 2 kN force were reported where composite side dams of the present invention were used.

In FIG. 13 an average of 21.27 snake eggs and a spread of 17 to 25 snake eggs of between 3 and 6 kN force were reported for campaigns where side dams of the previous solid design (or standard) were used. Whereas, the average number of snake eggs was 2.75 and a spread of 1 to 5 snake eggs of between 3 and 6 kN force where composite side dams of the present invention were used.

In FIG. 14 an average of 3.66 snake eggs and a spread of 3 to 4.3 snake eggs of greater than 5 kN force were reported for campaigns where side dams of the previous solid design (or standard) were used. Whereas, the average number of snake eggs of 0.51 and a spread of 0.2 to 0.8 snake eggs of greater than 5 kN force were reported where composite side dams of the present invention were used.

The increase in yield was also dramatic between the use of the previous solid standard side dams and the composite side dams of the present invention. The comparative results are set forth in Tables 1 and 2 below. Table 2 shows an increased in yield when composite side dams were used compared to side dams of the previous solid design (Table 1) in both prime from liquid metal and prime from coiled. Out of the eight comparative sequences presented, five of the comparative runs encountered problems at the end of the casting, such as: choking, snakes eggs, and coiler issues. No major problems were present in the sequences performed using composite side dams of the present invention.

TABLE 1 Prime Prime Secondary/ from from Seq Liquid Coiled Prime (tons) Scrap coiled liquid 6923 581 539 509.9 29.5 95% 88% 6924 347 322 292.2 29.6 91% 84% 6925 585 551 498.5 52.1 91% 85% 6926 536 236 215.4 20.8 91% 40% 6927 347 322 309.0 12.9 96% 89% 6928 574 437 413.7 23.1 95% 72% 6929 347 319 292.4 26.9 92% 84% 6943 452 427 389.6 37.5 91% 86% 3767 3153 2920.7 232.4 93% 78%

TABLE 2 Prime Prime Secondary/ from from Seq Liquid Coiled Prime (tons) Scrap coiled liquid 6937 553 518 496.3 21.7 96% 90% 6938 335 314 306.8 7.4 98% 92% 6939 327 307 296.1 10.8 96% 90% 6940 548 518 495.6 22.0 96% 90% 6941 563 533 524.3 8.2 98% 93% 6942 555 528 512.7 15.0 97% 92% 6944 348 319 304.3 14.9 95% 87% 6945 459 338 295.9 41.7 88% 64% 3689 3374 3232.0 141.7 96% 88%

As seen from the data above, a significant improvement in yield was reported for castings performed with composite side dams. The casting sequences performed using side dams of the previous solid design produced an average yield of 78%. As presented in Table 2, the casting sequences performed using composite side dams of the present invention produced a 10% yield increase for an average yield of 88%.

While it has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings without departing from its scope. Therefore, it is intended that it not be limited to the particular embodiments disclosed, but that it will include all embodiments falling within the scope of the appended claims. 

What is claimed is:
 1. A composite side dam for a continuous twin roll caster comprising: (a) a substrate shaped to form a side dam and made of a refractory material capable of withstanding casting temperature in a twin roll caster and having edge portions adapted to engage end portions of casting rolls and having a nip portion adapted to be adjacent a nip between casting rolls and upper portions extending across the side dam to form a lateral restraint for a casting pool of molten metal during operation in a twin roll caster, (b) an insert of at least 10 mm in thickness positioned in a pocket in the substrate and extending to engage the molten metal in operation of a twin roll caster and extending from the upper portions of the substrate such that the insert can be positioned in the pocket to within 30 mm from the nip portion of the substrate by insertion adjacent the upper portions of the substrate to engage end portions of the casting rolls during operation of the twin roll caster, and (c) the insert adapted to fit into the pocket of the substrate to form a side dam formed of a refractory material having consumption rate less than 10 mm per hour.
 2. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the material forming the insert is comprised of SiAlON material.
 3. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the material forming the insert is between 40 and 60% SiAlON material and the remainder hBN material.
 4. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the material forming the insert is comprised of mullite material as described by FIG.
 11. 5. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the material forming the insert is between about 60 and 63 mole percent Al₂O₃ and the remainder SiO₂.
 6. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the material forming the insert is comprised of fused silica material.
 7. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the material forming the insert is between 40 and 60% fused SiO₂ and the remainder hBN material.
 8. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the consumption rate of the refractory material forming the insert is at least as great as the wear rate of said material.
 9. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the insert is between 10 mm and 40 mm in thickness.
 10. The composite side dam for a continuous twin roll caster as claimed in claim 2 where the insert is between 10 mm and 40 mm in thickness.
 11. The composite side dam for a continuous twin roll caster as claimed in claim 4 where the insert is between 10 mm and 40 mm in thickness.
 12. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the insert is between 10 mm and 40 mm in thickness.
 13. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the insert is a firm fit positioned in the pocket.
 14. The composite side dam for a continuous twin roll caster as claimed in claim 2 where the insert is a firm fit positioned in the pocket.
 15. The composite side dam for a continuous twin roll caster as claimed in claim 4 where the insert is a firm fit positioned in the pocket.
 16. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the insert is a firm fit positioned in the pocket.
 17. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 18. The composite side dam for a continuous twin roll caster as claimed in claim 2 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 19. The composite side dam for a continuous twin roll caster as claimed in claim 4 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 20. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 21. The composite side dam for a continuous twin roll caster as claimed in claim 13 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 22. The composite side dam for a continuous twin roll caster as claimed in claim 14 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 23. The composite side dam for a continuous twin roll caster as claimed in claim 15 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 24. The composite side dam for a continuous twin roll caster as claimed in claim 16 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 25. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the insert is positioned in the pocket with a ceramic cement.
 26. The composite side dam for a continuous twin roll caster as claimed in claim 2 where the insert is positioned in the pocket with a ceramic cement.
 27. The composite side dam for a continuous twin roll caster as claimed in claim 4 where the insert is positioned in the pocket with a ceramic cement.
 28. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the insert is positioned in the pocket with a ceramic cement.
 29. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the thickness of the insert is greater than depth of the pocket.
 30. The composite side dam for a continuous twin roll caster as claimed in claim 2 where the thickness of the insert is greater than depth of the pocket.
 31. The composite side dam for a continuous twin roll caster as claimed in claim 4 where the thickness of the insert is greater than depth of the pocket.
 32. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the thickness of the insert is greater than depth of the pocket.
 33. The composite side dam for a continuous twin roll caster as claimed in claim 1 where the insert extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 34. The composite side dam for a continuous twin roll caster as claimed in claim 2 where the insert extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 35. The composite side dam for a continuous twin roll caster as claimed in claim 4 where the insert extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 36. The composite side dam for a continuous twin roll caster as claimed in claim 6 where the insert extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 37. Apparatus for continuously casting metal strip comprising: (a) a pair of counter-rotatable casting rolls laterally positioned to form a nip there between through which thin strip can be cast, (b) a pair of confining side dams adjacent the ends of the casting rolls capable of confining a casting pool of molten metal supported on the casting rolls and formed on the casting surfaces above the nip, (c) each side dam is a composite comprising a substrate made of a refractory material capable of withstanding casting temperature and extending from the upper portions of the substrate to a nip portion adapted to be adjacent a nip between casting rolls and such that the insert can be positioned in the pocket by insertion adjacent the upper portions of the substrate to engage end portions of the casting rolls to within 30 mm from the nip portion of the substrate during operation of the twin roll caster, and an insert of at least 10 mm in thickness positioned in a pocket in the substrate and extending to engage the molten metal and the end portions of the casting rolls in operation of the twin roll caster, and the insert adapted to fitted into the pocket of the substrate to form the side dam formed of a material having a consumption rate less than 10 mm per hour, and (d) a metal delivery system disposed above the nip and capable of discharging molten metal to form the casting pool supported on the casting rolls.
 38. The apparatus for continuously casting metal strip as claimed in claim 37 where the material forming the insert of the substrate is comprised of SiAlON material.
 39. The apparatus for continuously casting metal strip as claimed in claim 37 where the material forming the insert of the substrate is between 40 and 60% SiAlON material and the remainder hBN material.
 40. The apparatus for continuously casting metal strip as claimed in claim 37 where the material forming the insert is mullite material as defined by FIG.
 11. 41. The apparatus for continuously casting metal strip as claimed in claim 37 where the material forming the insert between about 60 and 63 mole percent Al₂O₃ and the remainder SiO₂.
 42. The apparatus for continuously casting metal strip as claimed in claim 37 where the material forming the insert of the substrate is comprised of fused silica material.
 43. The apparatus for continuously casting metal strip as claimed in claim 37 where the material forming the insert of the substrate is between 40 and 60% fused SiO₂ and remainder hBN material.
 44. The apparatus for continuously casting metal strip as claimed in claim 37 where the consumption rate of the refractory material forming the insert is at least as great as the wear rate of said material.
 45. The apparatus for continuously casting metal strip as claimed in claim 37 where the insert of the substrate is between 10 mm and 40 mm in thickness.
 46. The apparatus for continuously casting metal strip as claimed in claim 38 where the insert of the substrate is between 10 mm and 40 mm in thickness.
 47. The apparatus for continuously casting metal strip as claimed in claim 40 where the insert of the substrate is between 10 mm and 40 mm in thickness.
 48. The apparatus for continuously casting metal strip as claimed in claim 42 where the insert of the substrate is between 10 mm and 40 mm in thickness.
 49. The apparatus for continuously casting metal strip as claimed in claim 37 where the insert is a firm fit positioned in the pocket of the substrate.
 50. The apparatus for continuously casting metal strip as claimed in claim 38 where the insert is a firm fit positioned in the pocket of the substrate.
 51. The apparatus for continuously casting metal strip as claimed in claim 40 where the insert is a firm fit positioned in the pocket of the substrate.
 52. The apparatus for continuously casting metal strip as claimed in claim 42 where the insert is a firm fit positioned in the pocket of the substrate.
 53. The apparatus for continuously casting metal strip as claimed in claim 37 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 54. The apparatus for continuously casting metal strip as claimed in claim 38 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 55. The apparatus for continuously casting metal strip as claimed in claim 40 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 56. The apparatus for continuously casting metal strip as claimed in claim 49 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 57. The apparatus for continuously casting metal strip as claimed in claim 50 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 58. The apparatus for continuously casting metal strip as claimed in claim 51 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 59. The apparatus for continuously casting metal strip as claimed in claim 55 where the insert has edge portions of a reverse angle of at least 3° to engage edge portions of the pocket in the substrate.
 60. The apparatus for continuously casting metal strip composite side dam as claimed in claim 37 where the insert of the substrate is positioned in the pocket with a ceramic cement.
 61. The apparatus for continuously casting metal strip as claimed in claim 38 where the insert of the substrate is positioned in the pocket with a ceramic cement.
 62. The apparatus for continuously casting metal strip as claimed in claim 40 where the insert of the substrate is positioned in the pocket with a ceramic cement.
 63. The apparatus for continuously casting metal strip as claimed in claim 42 where the insert of the substrate is positioned in the pocket with a ceramic cement.
 64. The apparatus for continuously casting metal strip as claimed in claim 37 where the thickness of the insert of the substrate is greater than depth of the pocket.
 65. The apparatus for continuously casting metal strip as claimed in claim 38 where the thickness of the insert of the substrate is greater than depth of the pocket.
 66. The apparatus for continuously casting metal strip as claimed in claim 40 where the thickness of the insert of the substrate is greater than depth of the pocket.
 67. The apparatus for continuously casting metal strip as claimed in claim 42 where the thickness of the insert of the substrate is greater than depth of the pocket.
 68. The apparatus for continuously casting metal as claimed in claim 37 where the insert of the substrate extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 69. The apparatus for continuously casting metal as claimed in claim 38 where the insert of the substrate extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 70. The apparatus for continuously casting metal as claimed in claim 40 where the insert of the substrate extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam.
 71. The apparatus for continuously casting metal as claimed in claim 42 where the insert of the substrate extends toward the nip portion to allow at least a 2.5 mm radius in the insert adjacent nip portions of the side dam. 